As photoconducting materials to be incorporated in electrophotographic photoreceptors there have heretofore been used inorganic photoconductive substances such as selenium, cadmium sulfide, zinc oxide and amorphous silicon. These inorganic photoconductive substances are advantageous in that they have excellent electrophotographic properties. In particular, these inorganic photoconductive substances exhibit an excellent photoconductivity, charge acceptability in a dark place and insulating properties. On the contrary, however, these inorganic photoconductive substances have various disadvantages. For example, these photoreceptors are expensive to manufacture, can cause a pollution problem, have no flexibility and cannot withstand thermal or mechanical shock.
In recent years, electrophotographic photoreceptors comprising various organic photoconductive substances have been studied and proposed to eliminate these disadvantages of such inorganic photoconductive materials.
Most organic electrophotographic photoreceptors are lamination type photoreceptors having an electrically conductive support comprising at least two years, i.e., charge-generating layer which generates charge carriers upon exposure and charge-transporting layer which transports charge carriers. The charge-transporting layer essentially consists of a charge-transporting substance which transports charge carriers which have been generated in the charge-generating layer and then injected into the charge-transporting layer and a resin binder.
Such a charge-transporting substance is required (a) to sufficiently transmit light which has been absorbed by a charge-generating agent to allow the charge-generating substance to efficiently generate an electric charge, (b) to be sufficiently charged, and (c) to have a capability of having a charge carrier generated from the charge-generating substance efficiently injected thereinto to readily transport an electric charge.
There have been proposed many chargetransporting compounds such as triphenylmethane compounds as disclosed in JP-B-45-555 (the term "JP-B" as used herein means an "examined Japanese patent publication"), hydrazone compounds as disclosed in JP-B-55-42380, and JP-A-54-150128 (the term "JP-A" as used herein means an "unexamined published Japanese patent application" ), and triarylamine compounds as disclosed in JP-B-58-32372. Some photoreceptors comprising such a charge-transporting compound exhibit relatively excellent electrophotographic properties. However, these photoreceptors are disadvantageous in that they exhibit an insufficient sensitivity and a low durability to light or electric load and suffer from unstability and deterioration of properties upon repeated use. Therefore, these photoreceptors cannot sufficiently meet practical requirements. Thus, it has been desired to provide a charge-transporting compound which is more capable of transporting an electric charge and exhibits stable properties after a prolonged use.
As a result of extensive study, the inventors found that an acetylene compound represented by general formula (I) serves effectively as a charge-transporting compound in electrophotographic photoreceptors. Thus, the present invention was worked out.